1. Field of the Invention
The present invention relates to an image processing apparatus and an image processing method, and more particularly to an image processing apparatus and an image processing method having a function that corrects a signal that is output from a defective pixel.
2. Description of the Related Art
Image processing apparatuses such as an electronic camera which uses a memory card having a solid-state memory element as a recording medium, and records and plays back still images and moving images sensed by a solid-state image sensing device such as a CCD or a CMOS are already on the market.
It is known that when sensing an image using a solid-state image sensing device such as a CCD or a CMOS, image quality degradation occurs due to dark current noise generated by the image sensing device, a defective pixel that is unique to the image sensing device, or the like.
A conventional method of correcting such defective pixels involves assessing the output for a standard charge accumulation time under a predetermined condition at the time of factory shipment of the sensor, and determining whether pixels are defective based on the assessment results. Further, data regarding the kind of defect (a black defect, a white defect, or the like), the address, and the defect level of the relevant pixel is obtained, and the defective pixel is corrected using the data.
However, it is known that the degree of a defective pixel varies significantly depending on the conditions when sensing an image. Accordingly, for example, even in the case of a pixel that does not constitute a problem when performing general image sensing at a normal high shutter speed, the level thereof as a defective pixel increases when image sensing is performed at a slow shutter speed, and the pixel adversely affects the image quality. To avoid this problem, Japanese Patent Laid-Open No. 2005-175987 discloses technology that corrects defective pixels by taking into consideration the temperature of the image sensing device, the shutter speed and the sensitivity as conditions at the time of image sensing.
In this case, if a defect is a so-called “white defect”, as described in Japanese Patent Laid-Open No. 2005-175987, it is possible to define assessment conditions by taking into consideration the temperature, the shutter speed and the sensitivity. However, the kind of defective pixel is also an important factor. For example, some defective pixels are only affected by the sensitivity and are not affected at all by the exposure time (such defective pixels are referred to as a so-called “blinking defect”). In such a case, it is necessary to perform correction processing for the defective pixel at a time of a high sensitivity. However, appropriate conditions cannot be established based on assessment conditions that take into consideration the temperature and exposure time in addition to the sensitivity that are set for a white defect, and consequently, depending on the imaging conditions, there is the possibility that such defective pixels will be overcorrected or will not be corrected at all. Therefore, in some cases the image quality of a sensed image is degraded.